One method of producing photovoltaic arrays for the conversion of solar energy into electrical energy is to embed silicon particles in a matrix where the silicon particles have a outside coating of one conductivity type and an inside of an opposite conductivity type. Contact is made to the inside portion of the sphere on the back of the solar array and electrical energy is produced when photons of light strike the silicon particle and induce electrons to cross the depletion region between the two conductivity types. See Ralph, U.S. Pat. No. 3,025,335 entitled "Flexible Solar Energy Converter Panel", issued Feb. 29, 1962. As the solar array disclosed in Ralph was developed, it was determined that the optimum shape for the embedded silicon particles was spherical and that fabrication of the solar array was facilitated if the spherical silicon particles were of a uniform size.
Previous methods of fabricating silicon spheres of high purity and uniform size involved shotting of molten purified silicon out of a nozzle or out of a rotating disc. The spheres as formed in this manner are highly irregular in shape and polycrystalline. They can be made crystalline with the use of another process, involving heating of the material above the melting point. See Levine et al., U.S. Pat. No. 4,425,408, entitled "Production of Single Crystal Semiconductors", issued Jan. 10, 1984.
This sequence of shotting and remelting has the drawbacks that the silicon must be relatively pure and the sizing is irregular. An object of the present invention is to provide a method of producing silicon spheres of uniform size directly from low grade metallurgical silicon, thus providing a fabrication process for producing uniform silicon spheres at less cost than methods known in the prior art.
In addition, the prior art processes cannot produce spheres of sufficiently uniform size because of the difficutly of shotting the source silicon into particles of uniform volume.